An anatomical view of a human stomach S and associated features is shown in FIG. 27. The esophagus E delivers food from the mouth to the proximal portion of the stomach S. The z-line or gastro-esophageal junction Z is the irregularly-shaped border between the thin tissue of the esophagus and the thicker tissue of the stomach wall. The gastro-esophageal junction region G is the region encompassing the distal portion of the esophagus E, the z-line, and the proximal portion of the stomach S.
Stomach S includes a fundus F at its proximal end and an antrum A at its distal end. Antrum A feeds into the pylorus P which attaches to the duodenum D, the proximal region of the small intestine. Within the pylorus P is a sphincter that prevents backflow of food from the duodenum D into the stomach. The middle region of the small intestine, positioned distally of the duodenum D, is the jejunum J.
When food is placed in the mouth, carbohydrates in the food are partially broken down by enzymes in saliva. After the food is swallowed it is turned to a liquefied mass (chyme) by the acids and enzymes within the stomach. The chyme moves from the stomach into the intestine, where the chyme is further digested and where the bulk of the nutrients are absorbed through the intestinal membranes into the circulatory system. Within the small intestine, nutrients are broken down by enzymes and secretions from the pancreas, liver, gallbladder, as well as those secreted by cells of the intestine. The intestinal walls are lined with villi—small projections that extend into the intestinal lumen. The presence of the villi facilitates absorption by increasing the surface area of the small intestine. Undigested chyme passes into the large intestine (colon), from which it is ultimately excreted.
Prior patents and applications assigned to the assignee of the present application disclose the use of elongated intestinal sleeves or tubes for inducing weight loss. For example, U.S. Pat. No. 6,675,809 entitled “Satiation Device and Methods” describes, among other things, a tube that may be positioned beyond the pyloris, such as in or near the duodenum. Post-pyloric sleeves of this type can be useful for preventing or limiting absorption of nutrients by the small intestine, thus triggering weight loss in the patient. Moreover, it has been reported that gastric bypass procedures in which a portion of the small intestine is bypassed can ameliorate Type 2 diabetes. F. Rubino et al, The Mechanism of Diabetes Control After Gastrointestinal Bypass Surgery Reveals a Role of the Proximal Small Intestine in the Pathophysiology of Type 2 Diabetes, Annals of Surgery, Vol. 243, Number 6, June 2006. Positioning a bypass sleeve of the type disclosed in the '809 patent in the small intestine of a patient can achieve the same therapeutic function in a much less invasive manner.